[Different Subtypes Caused by c.721C>T Substitution in the Exon 7 of ABO Gene].

Objective: To analyze the different subtypes caused by c.721C>T substitution in the exon 7 of the ABO gene, and to investigate the related molecular mechanism of different antigens expression.
Methods: ABO subtypes in 7 samples were identified by standard serological methods. The exons 6, 7, and adjacent intron of ABO gene were amplified by Polymerase Chain Reaction (PCR), and the PCR products were analyzed by direct DNA sequencing and cloning sequencing.
Results: ABO subtypes phenotypes were A _W (1 case), B _W (3 cases), AB _W (2 cases), A ₂ or A _int (1 case). The result showed that the 7th exon of ABO gene was c.721C>T variety based on A1.02, B1.01, and O.01.02; the alleles were AW.43（1 case）, BW.03（5 cases） and O.01.07（1 case）, ABO genotypes were ABO*AW.43/O.01.02 (1 case) , ABO*BW.03/O.01.02 (3 cases), ABO*A1.02/BW.03 (2 cases), and ABO*A2.05/O.01.07 (1 case).
Conclusion: c.721C>T substitution in the ABO gene causes p.Arg241Trp exchange resulting in the decreasing of GTA or GTB activities and weaker antigen expression. O.01.07 is a null allele which cannot form a functional catalytic enzyme has no effect on A ₂ subtype antigen expression.